Electrical circuit for synthetic testing of circuit interrupters and method of operation

ABSTRACT

The application relates to a high voltage generator for the socalled synthetic testing of circuit interrupters operating at high and very high voltages, such generator being used more particularly in a testing circuit of the current injection type, and capable of providing successively an injection current waveform and a transient recovery voltage waveform. The generator comprises an injection branch providing the injection current waveform and a regulating branch providing the transient recovery voltage waveform. The injection branch is formed by at least two groups of elements, each comprising a capacitance, an inductance and a spark gap in series forming a unit, and by a switching system for interconnecting the units in series, or in parallel, or in a combined series-parallel connection. The regulating branch is formed by at least two groups of elements, each comprising at least one capacitance and at least one resistor forming a unit, and by a switching system for interconnecting the units in series, or in parallel, or in a combined series-parallel connection.

United States Patent Inventor Appl. No.

Filed Patented Assignee Priority Vladislav Zajle Montreal, Province ofQuebec, Canada 822,161

May 6, 1969 Sept. 14, 1971 Hydro-Quebec Montreal, Quebec, Canada Apr.12, 1969 Canada ELECTRICAL CIRCUIT FOR SYNTHETIC TESTING OF CIRCUITINTERRUPTERS AND Primary Examiner-Roy Lake Assistant ExaminerE. R.LaRoche Attorney-Raymond A. Robic ABSTRACT: The application relates to ahigh voltage generator for the so-called synthetic testing of circuitinterrupters operating at high and very high voltages, such generatorbeing used more particularly in a testing circuit of the currentinjection type, and capable of providing successively an injectioncurrent waveform and a transient recovery voltage waveform. Thegenerator comprises an injection branch providing the injection currentwaveform and a regulating branch providing the transient recoveryvoltage waveform. The injection branch is formed by at least two groupsof elements, each comprising a capacitance, an inductance and a sparkgap in series forming a unit, and by a switching system forinterconnecting the units in series, or in parallel, or in a combinedseries-parallel connection. The regulating branch is formed by at leasttwo groups of elements, each comprising at least one capacitance and atleast one resistor forming a unit, and by a switching system forinterconnecting the units in series, or in parallel, or in a combinedseries-parallel connection.

PATENTEDSEPMIQYI 3604- 976 I sum 1 0F 6 INVENTOR Vludisluv ATTORNEY E LC filIlll lull |l. Illlll i .o I r.. -L

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. A & 2 7 W 7 Wm/ PIP/0R ART ATENIEI] SEP I 4 zen SHEET u 0F 6 o o a o mm w W 7 WWW/A A M A A2 A d W Vladislov ZAJIC w A M As it is well knownin the art, the synthetic testing circuits comprise two circuits: Thefirst one providing, in the interrupter under test, the required currentin principle until the time of the opening of the interrupter and iscalled the high current source, the second one providing the requiredvoltage across the terminals of the circuit interrupter in principleafter the interruption of the current and is called the voltage source.In certain known circuits, the operation of the two circuits mentionedabove overlap partially in the neighborhood of the passage of thecurrent through zero in such a way that the input of current from thehigh current source is transferred to the voltage source before thepassage of the current through zero. These circuits are known under thename of synthetic testing circuits of the current injection type. Theinvention relates to the voltage source of such synthetic testingcircuits which comprises an injection branch for providing the injectioncurrent and a regulating branch for providing the transient recoveryvoltage.

In the prior art, the voltage source of the synthetic circuits of thecurrent injection type consisted of a concentrated capacitance, aconcentrated inductance and a spark-gap. This solution was possible bythe means known in the art for voltages up to 400 or 500 kv.Nevertheless, even at these voltages and more particularly at highervoltages, serious problems have been encountered in the design of theinductances and of the spark-gaps caused by the critical potentialdistribution along the windings of the inductances and the prolongedfiring time of the spark-gaps at very high voltages. Similarly, for avery high power at intermediate voltages, the discharge current of thespark-gaps is so great that burning of the electrodes is a limitingfactor.

The object of the invention is to overcome the extreme difficultiesaccompanying the design of the elements of the testing circuits for veryhigh voltages and very high powers while being also useful in theintermediate range of voltages and powers.

The high voltage generator, in accordance with the invention, is usedfor the socalled synthetic testing of circuit interrupters, and moreparticularly with a testing circuit of the current injection typecapable of providing successively an injection current wave and atransient recovery voltage wave. The generator comprises an injectionbranch providing the injection current wave and a regulating branchproviding the transient recovery voltage.

The basic idea of the invention is to form the injection branch by meansof at least two groups of elements, each comprising a capacitance, aninductance and a spark-gap in series forming a unit, and to provide theinjection branch with a switching system capable of connecting the unitsin series, in parallel, or in a combined series-parallel connection.

Similarly, the regulating branch is formed by at least two groups ofelements, each comprising at least one capacitance and at least oneresistor forming a unit. A switching system is used to connect the unitsin series, in parallel, or in a combined series-parallel connection in away similar to the injection branch.

It is also advantageous to have the same number of units in series or inparallel in the injection branch and in the regulating branch and toform integrated units comprising the elements of both branches. Thisway, a single switching system may be used for connecting the integratedunits in series, in parallel or in a combined series parallelconnection.

In the integrated units, the regulating branch may be connected inparallel with the inductance, or with the inductancespark-gap group, orwith the capacitance-inductance-sparkgap group of the injection branch.Finally, the connection of the regulating branch with the injectionbranch may be formed by a combination of the above-mentionedconnections.

There are two ways of charging the capacitances in each of the units: Inthe first one, the units are connected in parallel by means of theswitching systems and the required connections to obtain the number ofunits in series or in parallel are done subsequently prior to effectingthe test. In the second one, the required connections of the units inseries or in parallel are done and the capacitances are subsequentlycharged through a system of charging resistors having a very high ohmicvalue.

A firing system is used for operating the spark-gaps, this system beingcapable of firing all the spark-gaps or a predetermined portion of thespark-gaps only at the same time.

The invention also relates to a method of operating the above-describedgenerator in which the units are in a parallel connection for apredetermined voltage but in which it is desired to make successivetests at different powers. In accordance with the invention, the numberof units required for providing the necessary power for each test isobtained by firing the spark-gaps of the corresponding units only, theother units remaining unoperated.

Following the same basic idea, plural identical generators adjusted forvarious testing powers may be used and, for successive test, thesegenerators may be energized individually or in parallel depending uponthe power required by firing the spark-gaps of the correspondinggenerators only.

In another method of operating the above-mentioned generator, pluralgenerators having identical powers but charged by voltages of oppositepolarities may be used, and the generators having alternate oppositepolarities may be operated successively in the successive passagesthrough zero of the high current source by firing the spark-gaps of thecorresponding generators.

Finally, in a further mode of operation of the above-mentionedgenerator, two identical groups of generators charged with voltages ofopposite polarities may be used, and such generators may be firedsimultaneously in series in a synthetic testing circuit so as to providea double transient recovery voltage on the terminals of the interruptersunder test.

The present invention will be more clearly understood by means of thefollowing description which refers to the accompanying drawings by wayof example only. In the drawings:

FIG. 1 illustrates a known synthetic circuit comprising a concentratedcapacitance, a concentrated inductance and a spark-gap,

FIGS. 2A and 2B illustrate the path of the currents and of the voltagesrespectively in the synthetic circuit of FIG. I during a test,

FIG. 3 illustrates a detailed diagram of the injection branch inaccordance with the invention,

FIG. 4 illustrates a detailed diagram of the regulating branch inaccordance with the invention, 7

FIGS. 5A and 5B illustrate respectively a synthetic circuit in which theinjection branch is combined with the regulating branch, FIG. 5Billustrating a circuit having concentrated elements and FIG. 5Aillustrating a circuit in accordance with the invention,

FIG. 6 illustrates a synthetic circuit having integrated units and asingle switching system,

FIGS. 7 to II illustrate other arrangements of integrated units inaccordance with the invention,

FIG. 12 illustrates a generator comprising six units in series in whichthe two upper units use a different method of regulating the transientrecovery voltage,

FIG. 13 illustrates a method of operation of a high voltage generatorhaving plural units in parallel, and

FIGS. 14 and I5 illustrate a method of operation of a high voltagegenerator formed of plural generators in parallel.

FIG. 1 illustrates a diagram of a conventional synthetic circuitcomprising a high current circuit at the industrial frequency composedof a current source I, a closing switch 2, an auxiliary circuit breaker3 and a circuit breaker under test 4. The current source 1 illustratedhere as being a transformer may, of course, be an alternator, a powersystem, or an oscillating circuit LC providing the industrial frequencycurrent. To the terminals of the circuit breaker under test is connecteda second circuit, called a high voltage source, which comprises aninjection branch and a regulating branch 6. In the illustrated example,the injection branch 5 comprises a capacitance C, and inductance L and aspark-gap E in series and the regulating branch 6 comprises a resistor Rand a capacitance C also connected in series.

The operation of this simplified circuit is illustrated in FIGS. 2A and2B in which the current waveforms may be seen on the time axis of FIG.2A and the voltage waveforms may be seen on the time axis of FIG. 2B.Before starting the test, the current source 1 is energized, the closingswitch 2 is opened, the circuit breakers 3 and 4 are closed, and theconcentrated capacitance C of injection branch 5 is charged by means ofa charger which is not shown. When closing switch 2 is closed, a currentat the industrial frequency of 60 Hz. starts to flow in the high currentcircuit. The curve 7 of FIG. 2A illustrates the last half-period of thiscurrent before the opening of the circuit breakers. At a predeterminedlocation before point 8 on the time axis, the contacts of the twocircuit breakers 3 and 4 are opened and two arcs in series are formed inthe high current circuit. At point 8 which represents a suitable timebefore point 9 representing the passage to zero of current 7, thespark-gap E of the injection branch 5 illustrated in FIG. 1 is tired anda second current 11, called the injection current, starts to flow in theinjection branch and through the circuit breaker 4 under test. The twocurrents are added in the circuit breaker 4 to produce the waveform 12between points 8 and 9 on the time axis, while current 7 only flowsthrough the auxiliary circuit breaker 3. The auxiliary circuit breaker 3cuts the current waveform 7 at point 9 so that the high current circuitis separated from this point from the high voltage circuit. In the timeinterval 9-l0 before the passage to zero of current waveform 11, thecurrent in the circuit breaker 4 under test is provided by the highvoltage source only, that is by the injection branch 5.

In FIG. 2B, which illustrates the voltage path, the DC voltage of theconcentrated capacitance C in injection branch 5 is shown by thestraight portion of curve 13. From point 8 on the time axis, whenspark-gap E is fired, until point 10, such voltage is invertedcorresponding to the half-period of the injection current 11 due to theoscillating circuit LC of the injection branch 5, so that the voltage ofthe concentrated capacitance C of the injection branch 5 is given bypoint 14 at time 10. The voltage on the terminals of circuit breaker 4until time was practically zero because, with modern circuit breakersoperating at very high voltages, the arc voltage is only about I to 2percent of the nominal voltage. At point 10 on the time axis, theinjection current loop is opened by circuit breaker 4 and the regulatingbranch 6, which was short-circuited by the are at the terminals ofcircuit breaker 4, comes into play. A new oscillating circuit is formedby the injection branch 5 and the regulating branch 6 in series. Theequilibrium of the voltages on the concentrated capacitances C of thetwo branches gives the oscillations of the transient recovery voltage 16on the circuit breaker 4 under test. The transient recovery voltage 16is superposed on the voltage 13, and the hatched surface between the twocurves gives the voltage on the concentrated inductance L of injectionbranch 5.

FIG. 3 illustrates an example of a detailed connection of the injectionbranch in accordance with the invention. There is shown, by way ofexample, six identical units 31 to 36 each composed of a capacitance 37,an inductance 38 and a sparkgap 39 in series. Between each pair of units31 to 36, is located a system of switches 40, 41 and 42 which permit toconnect the units in series, or in parallel, or in a combinedseries-parallel connection. If the switches 40 and 42 are closed, theunits are connected in parallel; if switches 41 only are closed, theunits are connected in series. This way, there may be obtained a numberof connections such as, for example, six units in parallel, three unitsin parallel in series with three other units in parallel, three seriescircuits of two units in parallel, or finally six units in series. It isobvious that the number of units illustrated in FIG. 3 may vary andthat, by operating predeter mined switches, four or five units in seriesmay be obtained by shunting two or one units respectively. The use ofthe three elements in each unit, that is of capacitance 37, ofinductance 38 and of spark-gap 39, as well as the injection frequency isalways the same whatever may be the connection of the units.

The groups capacitances-inductances 37-38 in all the units 31 to 36 areconnected in parallel through charging resistors 43 and 44 having a veryhigh ohmic value. The whole assembly is grounded at point 45 andconnected to a charger at terminal 47 through a further resistor 46.

The simultaneous firing of spark-gaps 39 in all the units is done bymeans of a system 48, illustrated in dash lines, which does not formpart of the present invention.

The operation of the injection circuit disclosed in FIG. 3 is asfollows:

First of all, the capacitances 37 in all the units are charged by meansof a charger connected to terminal 47. Charging of the capacitances maybe done in two ways: The first one consists in connecting the units inparallel by means of switches 40 and 42 to charge the capacitances.Subsequently, the preselection of the connection of the units 31 to 36is done by means of the system of switches 40 to 42. The second oneconsists in effecting the required connections and then to charge thecapacitances through the charging resistors 43 and 44. At a suitabletime 8 (FIGS. 2A and 28), a pulse is simultaneously applied to all thespark-gaps 39 by firing system 48 and arcs are triggered between theelectrodes of the spark-gaps. At this time, the preselected connectionis realized and the circuit starts to furnish a half-period of theinjection current in the circuit breaker under test as shown by curve 11in FIG. 2A.

FIG. 4 illustrates a detailed diagram of the regulating branch 6 ofFIG. 1. By way of example, there is shown the same number of units as inFIG. 3, that is six units identified by reference numerals 51 to 56.Also by way of example, it is seen that the six units are composed eachof a capacitance 57 in series with a resistor 58, this group beingshunted by another capacitance 59. The different units 51-52, 52-53,etc. are connected by a system of switches 60, 61 and 62 in the same wayas in FIG. 3, permitting a series, parallel, or seriesparallelconnection of the units.

As it has been mentioned previously, the purpose of the regulatingbranch is to influence the form of the transient recovery voltage (FIG.2B) and more particularly its frequency, its amplitude and the steepnessof the waveform thereof. At the time of making the connections of thisbranch, as it has been illustrated previously, the values of thecapacitances and of the resistors are adjusted coarsely to therespective testing voltages. Only a fine regulation remains to be donewithin desired limits for a predetermined testing voltage. At the sametime, an alternate arrangement of the resistors and of the capacitancesgives a more regular distribution of the voltage along the units, whichpermits a more economical design.

FIG. 5A illustrates the injection branch and the regulating branch ofFIGS. 3 and 4 interconnected together, but free of all the technicaldetails, and shows the principal elements connected in series. The twobranches represent the high voltage source corresponding to branches 5and 6 of FIG. 1. FIG. 58 illustrates a diagram of an equivalent circuitbut with concentrated elements. The following lines will establish acomparison between some voltage values which influence the spacing ofthe elements in the circuits of FIG. 5A and FIG. 58

respectively, assuming that the testing voltage and power are the samefor both circuits.

Before triggering the spark-gap in FIG. 5B, the point 70 andconsequently the whole regulating branch is at ground potential becausethe circuit breaker under test has not yet extinguished the electric arebetween its contacts. The battery of capacitances 71 is charged at thefull voltage, so that the insulating distances between the terminal 72,the inductance 73, the electrode 74 of the spark-gap and the remainingelements of the circuit must be maintained.

During the injection period, the potential of point 70 of the regulatingbranch remains always at a potential which is near ground potential. Inthe injection branch, the electrodes of the spark-gap being shunted byan electric arc, an oscillating current flows producing a voltage dropin inductance 73 always equal to that across capacitance 71. This meansthat during the injection period an oscillating voltage having a peakvalue equal to the charge voltage of capacitor 71 remains betweenterminal 72 and the rest of the circuit. The conditions for theinsulating distances are then substantially the same as during thepreceding period.

After the opening of the current loop in the circuit breaker under test,a voltage equilibrium occurs such as illustrated in FIG. 2B. The curve16 of FIG. 28 represents the potential of point 70 of FIG. 5B, the curve13 the potential of point 72, while the hatched surface 15 representsthe voltage between the terminals of inductance 73 in FIG. 5B.Consequently, during this period also, the insulating distances must bemaintained between the various points of the circuit. It is only afterthe expiration of the transientperiod that the situation is simpler,points 70 and 72 being then at the same potential. In conclusion, it maybe seen that, in FIG. 5B, adequate distances must be maintained betweencertain points of the circuit which impose severe conditions on thespace occupied by the circuit.

For the diagram illustrated in FIG. 5A, which is composed of identicalunits, points 81 to 85 are almost at ground potential, if the arcvoltage across the circuit breaker under test is neglected, during thefull period until the point where the spark-gap is triggered. In theinjection branch, the capacitances of the different units are allcharged by a voltage equal to one-sixth, in our example, of thepotential which exists at point 72 of FIG. 5B. This means that points 86to 90 which are normally connected by charging resistors (see FIG. 3)are at ground potential, and that points 91 to 96 which are alsoconnected by charging resistors (see FIG. 3) are at potential higherthan ground potential but equal between each other, that is one-sixth ofthe total voltage. In conclusion, all the points 81 to 90 arepractically at ground potential and it is not necessary to maintain anyinsulating distances between them.

During the injection period, the situation does not change very much.The regulating branch remains always short-circuited by the circuitbreaker under test and the potential along the six units issubstantially equal to ground potential. In the injection branch, thespark-gaps being shunted by the arcs across their terminals, a currentflows through all the capacitances and through all the inductances, thecircuit being closed by the circuit breaker under test. This currentcauses the formation of positive voltages on the capacitances and ofnegative voltages on the inductances which are equal in value but are ofopposite sign. By adding these positive and negative potentials, it maybe seen that the voltages are cancelled on each pair ofcapacitance-inductance and that the potentials of points 86 to 90 arealways the same and equal to ground potential. We must then come to theconclusion, which may seem odd, that the potentials of all the points 81to 85 of the regulating branch and the ones of points 86 to 90 of theinjection branch are equal.

Finally, during the period after the opening of the current loop in thecircuit breaker under test, a new oscillating circuit is formedcomprising only the two branches illustrated in FIG. 5A. An oscillatingcurrent flows in the circuit producing the total voltage of point 80with respect to ground illustrated by curve 16 in FIG. 213. But,whatever may be the instantaneous voltage between point 80 and ground,such voltage is divided in the same proportions along the units of theregulating branch as along the units of the injection branch, so thatthe potentials of points 81-86, 82-87, 83-88, 84-89 and 85-90 correspondwhile increasing with respect to ground potential.

Consequently, direct connections may be made between the above-mentionedpoints as illustrated in dash lines in FIG. 5A. This way, the twobranches may be combined and form integrated units comprising aninjection branch and a regulating branch in each unit.

The formation of integrated units causes the automatic elimination of aseparate switching system for the regulating branch because the requiredswitching may be done by the system of the injection branch. Two unitsin accordance with the above-mentioned proposition, with a singleswitching system is illustrated in FIG. 6 in which the thick linesrepresent the injection branches and the fine lines the regulatingbranches. By means of switches and 101, the two units illustrated may beconnected in parallel or in series. By adding a suitable number ofunits, there may be obtained a complete high voltage source foreffecting the synthetic tests.

FIGS. 5A and 6 illustrate an example of high voltage source based on theunit concept for the regulation of the transient recovery voltage bymeans of a regulating branch connected in parallel with the fullinjection branch composed of a capacitance, an inductance and aspark-gap. However, the other known regulating methods may equally usethe unit concept in accordance with the invention. FIG. 7 illustrates aregulating branch comprising a capacitance 104 and a resistor 105 inseries and another capacitance 106 in parallel which is connected inparallel with inductance 107 only of the injection branch.

FIG. 8 illustrates another embodiment of a regulating branch comprisinga capacitance 108 and a resistor 109 in series and another capacitance110 connected in parallel which is connected in parallel with the groupinductance-spark-gap of the injection branch. This circuit offers a moreeconomical solution because the regulating capacitances 108 and 110 areprecharged with capacitance C of the injection branch through thecircuit breaker under test. The amount of energy contained in thecircuit is consequently higher and provides a testing power which isgreater. It is obviously possible to combine the regulating methodsillustrated in FIGS. 6, 7 and 8. An example of such a combination of theregulating method of FIG. 6 together with the regulating method of FIG.8 is illustrated in FIG. 9.

In FIG. 10, the regulating branch comprises a first portion including acapacitance I11 and a resistor 112 connected in parallel with aninductance 113 of the injection branch and a second portion including acapacitor 114 connected in parallel with the group inductance-spark-gapof the injection branch. In FIG. 11, the regulating branch comprises afirst portion including a capacitance 115 and a resistor 116 connectedin parallel with an inductance 117 of the injection branch, and a secondportion including a capacitance 118 connected in parallel with the groupcapacitance-inductancespark-gap of the injection branch.

Up to now, there has been disclosed a unit concept for a high voltagesource composed of identical units. However, the unit concept disclosedpermits to obtain other results which were not obtainable withconventional circuits, or which presented problems which were difficultto resolve. With the unit concept, it is possible to connect in seriestwo groups of units such as illustrated in FIGS. 6 to 11 having twodifferent inherent frequencies, or even to use, in two groups, unitshaving different methods of regulating the transient recovery voltage.For example, there is illustrated in FIG. 12 a circuit composed of sixunits 121 to 126. The two upper units 121 and 122 use a method ofregulating the transient recovery voltage which is different from theunits 123 to 126. Infact, the injection branches comprising thespark-gaps, the inductances, and the capacitances are exactly the samein each unit, but concerning the regulating branches, the capacitancesare smaller in the two upper units than in the four lower units. The twoparts of the high voltage source form two independent oscillatingcircuits producing a superposition of two oscillations, and the resultis a peculiar transient recovery voltage path composed of two differentfrequencies. In the example illustrated,

the circuit having a higher frequency is however more complex tofacilitate the adjustment of the shape of the transient recovery voltageimmediately after the opening of the current path through the circuitbreaker under test.

It is to be understood that, to obtain a transient recovery voltagehaving two or plural natural frequencies, different types of units suchas disclosed in FIGS. 6 to 11 may be combined, or even other connectionswhich may be simpler or more complex may be used.

The basic idea of the invention has been disclosed based on the diagramof a testing circuit such as in FIG. 1 which is known under the name ofparallel diagram. In a similar fashion, it is possible to a ply theconcept of the invention to other known testing methods such as theseries testing diagram.

The unit concept in accordance with the invention presents differentother possibilities which also form objects of the invention. Forexample, FIG. 13 illustrates a diagram of a high voltage generator forsynthetic testing comprising six units 141 to 146 having an internalconnection such as illustrated in FIGS. 6 to 11, and a triggering system147 for the spark-gaps. The units are connected in parallel and may beoperated as follows:

If the power generated by the complete generator is 100 percent, thetest may be started with onesixth of this power by sending a tiringimpulse to one spark-gap only, for example to the spark-gap of unit 141.By sending two firing pulses at the same time for a following test,there may be obtained onethird of the power, three pulses giving half ofthe power, etc. until the full power is generated. The above method ofusing the circuit is more economical because the power output of thegenerator may be changed by simply turning a button in the control room.Without this possibility, it would be necessary to change theconnections in the high voltage circuit, which, in the case of voltagesin the order of a few hundreds of kilovolts, is extremely laborious.

Another example is illustrated in FIG. 14. There is shown threegenerators 148, 149 and 150, the internal connection of which may beseries, parallel, or a combined series-parallel connection but identicalin the three generators. We may proceed as follows in this example:

First, the three generators are adjusted at different testing powers,for example percent of the full power for generator 148, 30 percent ofthe full power for generator 149 and 60 percent of the full power forgenerator 150. Then, by selecting suitable triggering pulses, thegenerators may be operated individually, or in parallel, depending onthe required power. Consequently, there may be obtained a series ofsuccessive powers for the test, for example 10 percent, 30 percent, 60percent and 100 percent as requested in the international regulations.Naturally the percentages and the number of generators used is disclosedby way of example only. It is obvi ous that other combinations areavailable.

Second, there may be used a certain number of generators, for examplethree such as illustrated in FIG. 14 in another fashion. Let us assumethat the three generators 148, 149 and 150 are adjusted at the samepower but have alternate polarities, for example that generator 148 hasa positive charge, 149 a negative charge and 150 a positive charge. Thethree generators may be operated successively during three successivepassages of the high current through zero while changing the polarity.This way, a circuit breaker may be tested with an arc lasting threehalf-periods. It is obvious that the number of generators, which hasbeen disclosed as being three, and that the number of successive zerosof the current, which have also been mentioned as being three, has beenchosen by way of example only and that a higher or a lower number may beused.

Another use of the generators is illustrated in FIG. 15. There isillustrated a synthetic testing circuit whereby it is possible to testcircuit breakers having a nominal voltage which is twice the voltage ofthe generators. The high current circuit is composed of a source 151 atthe industrial frequency, of two auxiliary circuit breakers 152 and 153and ofa single circuit breaker under test 154, having a nominal voltagewhich is twice the voltage of circuit breaker 152 and 153. Two syntheticgenerators 155 and 156 or two groups of generators, the first one beingcharged with a positive potential, the second one being charged with anegative potential, are used. At a suitable time before the passage ofthe high current through zero, exactly as illustrated in FIG. 2A, thespark-gaps in the two generators 155 and 156 are triggered and aninjection current (11 FIG. 2A) is circulated in circuit breaker 154 bythe two generators in series. The interruption of the current in thecircuit breaker under test is exactly the same as in FIG. 2A. After theinterruption of the current, the two generators produce two oscillationsof the transient recovery voltage, which are the same or differentdepending on the case under consideration, but have a different polaritywhich in being superposed give a double transient recovery voltage onthe terminals of the circuit breaker under test.

In concluding this description, the following advantages may bementioned concerning the generator in accordance with the invention:

l. By the application of the basic idea of the invention, there isobtained a synthetic testing circuit, and more particularly a highvoltage injection branch for such synthetic testing circuit, whileobviating the difficulties concerning the dielectric insulation of theinductances and spark-gaps used in the construction thereof.

2. By the application of the basic idea of the present invention, thereis obtained an injection branch which may be used for very high powersat intermediate voltages, while obviating the excessive burning of theelectrodes of the spark-gaps.

3. By applying the basic idea of the invention, there is obtained animportant advantage by choosing the voltage and the current in each unitin such a way as to correspond to the optimum use of the materials ofthe elements of the unit. There is then obtained not only a solutionwhich was not obtainable for extreme voltages and currents, that is inthe field where such solution was not obtainable by the means known tonow, but also a solution which is useable with a higher safety and ahigher economy in a field where such solution was useable by the meansknown up to now.

It may be also seen that by using a unit concept in the regulatingbranch, there may be obtained plural advantages on top of the onesmentioned above which are as follows:

1. First, by the series-parallel connection of the units, there isobtained a coarse regulation of the parameters. With the concentratedelements, it would have been necessary to have a separate switchingsystem for each element, that is, for the example disclosed, a switchingsystem for the capacitances and a switching system for the resistors.The first advantage of the proposed solution is consequently a switchingsystem which is more simple and consequently more economical.

2. Second, the regulating branch being composed of identical elements,it permits a more economical manufacture.

3. Third, the alternative arrangement of the resistors and thecapacitances give a more regular distribution of the voltage along theregulating branch, which also results in a more economical construction.

The integrated unit concept of the injection branch and of theregulating branch permits to interconnect these two branches and toobviate the insulating distances which would be necessary with thearrangement known to now and so result in a space saving, whichrepresents another advantage of the invention.

Finally, numeral other advantages of the generator in accordance withthe invention have been mentioned in the application and it would beobviously superfluous to give a complete list thereof because they havealready been mentioned.

lclaim:

1. High voltage generator used for the synthetic testing of high voltagecircuit interrupters, and more particularly for a testing circuit of thecurrent injection type, and capable of providing successively aninjection current waveform and a transient recovery voltage waveform,comprising:

a. an injection branch providing said injection current waveform and aregulating branch providing said transient recovery voltage waveform;

. the injection branch being formed by at least two groups of elements,each composed of a capacitance, an inductance and a spark-gap in seriesand forming a unit, and by a switching system for effecting apreselected connection of the units in series, or in parallel, or in acombined series-parallel relationship prior to the test of theinterrupters for providing an injection current waveform of a desiredform;

. the regulating branch being formed by at least two groups of elements,each composed of at least a capacitance and at least a resistor forminga unit, and by a switching system for effecting a preselected connectionof the units in series, or in parallel, or in a combined series-parallelrelationship prior to the test of the interrupters for providing atransient recovery voltage waveform of a desired form.

2. High voltage generator as defined in claim 1, in which thecorresponding units of the injection branch and of the regulating branchare interconnected to form integrated units comprising each the elementsof an injection branch and of a regulating branch and wherein a singleswitching system is provided for connecting the integrated units inseries, in parallel, or in a combined series-parallel connection.

3. High voltage generator as defined in claim 2, in which, in theintegrated units, the regulating branch is connected in parallel withthe inductance of the injection branch.

4. High voltage generator as defined in claim 2, in which, in theintegrated units, the regulating branch is connected in parallel withthe group inductance-spark-gap of the injection branch.

5. High voltage generator as defined in claim 2, in which, in theintegrated units, the regulating branch is connected in parallel withthe group capacitance-inductance-spark-gap of the injection branch.

6. High voltage generator as defined in claim 2, in which, in theintegrated units, the regulating branch comprises a first portionconnected in parallel with the inductance of the injection branch and asecond portion connected in parallel with the group inductance-spark-gapof the injection branch.

7. High voltage generator as defined in claim 2, in which, in theintegrated units, the regulating branch comprises a first portionconnected in parallel with the inductance of the injection branch and asecond portion connected in parallel with the groupcapacitance-inductance-spark-gap of the injection branch.

8. High voltage generator as defined in claim 2, in which, in

the integrated units, the regulating branch comprises a first portionconnected in parallel with the group inductancespark-gap of theinjection branch and a second portion connected in parallel with thegroup capacitance-inductancespark-gap of the injection branch.

9. A testing circuit including two identical generators as defined inclaim 1, charged with potentials of opposite polarities and connected inseries with a high current source through separate auxiliaryinterrupters, the interrupter under test being connected between twoterminals of opposite polarities of said generators, the generatorsbeing triggered simultaneously so as to form a double transient recoveryvoltage on the terminals of the interrupter under test.

10. High voltage generator as defined in claim 1, in which theregulating branch is formed of at least two groups of units in which thecapacitances are different producing at least two transient recoveryvoltages having their own inherent frequencies.

11. High voltage generator as defined in claim 1, comprising a systemfor triggering the spark-gaps which is capable of firing all thespark-gaps or a predetermined portion of the sparkgaps only at the sametime.

12. Method of simulating the required power for the synthetic testing ofhigh voltage circuit interrupters using a pluralit of generators eachincluding a plurality of generator units 0 the current injection type,and capable of providing successively an injection current waveform anda transient recovery voltage waveform, and comprising an injectionbranch and a regulating branch, the injection branch and the regulatingbranch being formed each by at least two groups of elements forming eacha generator unit, and by a switching system for connecting the generatorunits in series or in parallel, said method consisting in connecting inparallel plural identical generators and for successive tests energizinga different number of generators to provide the required power bytriggering the spark-gaps of the corresponding generators only.

13. Method of simulating the required power for the synthetic testing ofhigh voltage circuit interrupters using a plurality of generator unitsof the current injection type, and capable of providing successively aninjection current waveform and a transient recovery voltage waveform,and comprising an injection branch and a regulating branch, theinjection branch and the regulating branch being formed each by at leasttwo groups of elements forming each a generator unit, said methodconsisting in connecting the units in parallel, and in energizing asuitable number of units to provide the required power for the test bytriggering the spark-gaps of the corresponding units only.

1. High voltage generator used for the synthetic testing of high voltagecircuit interrupters, and more particularly for a testing circuit of thecurrent injection type, and capable of providing successively aninjection current waveform and a transient recovery voltage waveform,comprising: a. an injection branch providing said injection currentwaveform and a regulating branch providing said transient recoveryvoltaGe waveform; b. the injection branch being formed by at least twogroups of elements, each composed of a capacitance, an inductance and aspark-gap in series and forming a unit, and by a switching system foreffecting a preselected connection of the units in series, or inparallel, or in a combined series-parallel relationship prior to thetest of the interrupters for providing an injection current waveform ofa desired form; c. the regulating branch being formed by at least twogroups of elements, each composed of at least a capacitance and at leasta resistor forming a unit, and by a switching system for effecting apreselected connection of the units in series, or in parallel, or in acombined series-parallel relationship prior to the test of theinterrupters for providing a transient recovery voltage waveform of adesired form.
 2. High voltage generator as defined in claim 1, in whichthe corresponding units of the injection branch and of the regulatingbranch are interconnected to form integrated units comprising each theelements of an injection branch and of a regulating branch and wherein asingle switching system is provided for connecting the integrated unitsin series, in parallel, or in a combined series-parallel connection. 3.High voltage generator as defined in claim 2, in which, in theintegrated units, the regulating branch is connected in parallel withthe inductance of the injection branch.
 4. High voltage generator asdefined in claim 2, in which, in the integrated units, the regulatingbranch is connected in parallel with the group inductance-spark-gap ofthe injection branch.
 5. High voltage generator as defined in claim 2,in which, in the integrated units, the regulating branch is connected inparallel with the group capacitance-inductance-spark-gap of theinjection branch.
 6. High voltage generator as defined in claim 2, inwhich, in the integrated units, the regulating branch comprises a firstportion connected in parallel with the inductance of the injectionbranch and a second portion connected in parallel with the groupinductance-spark-gap of the injection branch.
 7. High voltage generatoras defined in claim 2, in which, in the integrated units, the regulatingbranch comprises a first portion connected in parallel with theinductance of the injection branch and a second portion connected inparallel with the group capacitance-inductance-spark-gap of theinjection branch.
 8. High voltage generator as defined in claim 2, inwhich, in the integrated units, the regulating branch comprises a firstportion connected in parallel with the group inductance-spark-gap of theinjection branch and a second portion connected in parallel with thegroup capacitance-inductance-spark-gap of the injection branch.
 9. Atesting circuit including two identical generators as defined in claim1, charged with potentials of opposite polarities and connected inseries with a high current source through separate auxiliaryinterrupters, the interrupter under test being connected between twoterminals of opposite polarities of said generators, the generatorsbeing triggered simultaneously so as to form a double transient recoveryvoltage on the terminals of the interrupter under test.
 10. High voltagegenerator as defined in claim 1, in which the regulating branch isformed of at least two groups of units in which the capacitances aredifferent producing at least two transient recovery voltages havingtheir own inherent frequencies.
 11. High voltage generator as defined inclaim 1, comprising a system for triggering the spark-gaps which iscapable of firing all the spark-gaps or a predetermined portion of thespark-gaps only at the same time.
 12. Method of simulating the requiredpower for the synthetic testing of high voltage circuit interruptersusing a plurality of generators each including a plurality of generatorunits of the current injection type, and capable of providingsuccessively an injection currenT waveform and a transient recoveryvoltage waveform, and comprising an injection branch and a regulatingbranch, the injection branch and the regulating branch being formed eachby at least two groups of elements forming each a generator unit, and bya switching system for connecting the generator units in series or inparallel, said method consisting in connecting in parallel pluralidentical generators and for successive tests energizing a differentnumber of generators to provide the required power by triggering thespark-gaps of the corresponding generators only.
 13. Method ofsimulating the required power for the synthetic testing of high voltagecircuit interrupters using a plurality of generator units of the currentinjection type, and capable of providing successively an injectioncurrent waveform and a transient recovery voltage waveform, andcomprising an injection branch and a regulating branch, the injectionbranch and the regulating branch being formed each by at least twogroups of elements forming each a generator unit, said method consistingin connecting the units in parallel, and in energizing a suitable numberof units to provide the required power for the test by triggering thespark-gaps of the corresponding units only.